[84 SOME SOI III INDIAN INSECTS, ETC. [CHAP. XX. 



mosquitos, fleas and bed-bugs, is perhaps hardly to be classed as a 

 disease, but it is often a serious source of annoyance, and abrasion of 

 the skin due to scratching or rubbing such bites may give entrance 

 to germs and thus set up blood-poisoning. The irritation caused 

 b\ such bites varies considerably in individuals and as regards the 

 bites of different classes of insects. In the case of mosquito-bites 

 the resultant irritation is usually most pronounced in the case of 

 new-comers into the tropics, a partial tolerance being acquired as a 

 rule alter a more or less brief period of residence, but the immunity 

 acquired against the bites in one locality is not always effectual in 

 another. Some people appear to be naturally or partially immune 

 from the irritant effects of bites, while others never become so. 

 The irritation is caused by a liquid injected, before the mosquito 

 actually commences to suck blood, not from the salivary glands as 

 would be expected, but from the oesophageal diverticula which 

 Schaudinn has shown to contain bubbles of Carbon Dioxide and 

 bacteria or moulds. Besides the irritation caused by single bites of 

 insects and their individual attacks on man and animals it is often 

 necessary to consider the serious effects wrought by the combined 

 effects of these attacks. Such a combined effect is called " mass 

 infection " and its results, by mere loss of blood and irritation, may 

 cause very serious effects on the health of the host even in the 

 absence of infection by pathogenic organisms. 



It is impossible within the limits of a single chapter to attempt 

 anj adequate description of the organisms which are the true 

 causes of many diseases or of the insects which carry them to man 

 and animals, but a short account of a few of the more important of 

 such insects will be found further on (see pages 346—367, 486-487, 

 521 — 5241. But before discussing the diseases, it may be as well to 

 give here a short account of some of the non-hexapod carriers. 



Ticks are distinguished from Hexapods by possessing four pairs 

 of legs in the adult state, although the newly-hatched immature 

 tick has only three pairs of legs but subsequently develops the 

 fourth (posterior) pair. Ticks belong to the group Acarina, which 

 rii ludes Mites and these latter are probably important as 

 disease-carriers also, although at present thej have been little 

 studied and ver\ little is known about them indeed, practically 

 nothing in India. 



The true Ticks form the superfamily bcodoidea, subdivided into 

 th( families Argasidse and [xodida?. The feeding-habits, which 

 are very important from a control view-point, are very varied in the 

 different groups ; in ome the tick remains attached to the host, 

 whilst in others it merely gorges itsell with blood and then drops 

 oft and hide-, until it again requires to feed. In different groups of 



